Fuller Lawns and Controlling Weeds
The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: I have approx 1.5 acres of lawn to take care of. My wife has occasionally called me obsessed with "yard work." I assure her that it's not an obsession it's stress relief. I'm probably 90% content with the appearance of the lawn although it isn't as full as I'd like it to be. In your paragraph about adding 1 lb N/1000 square foot, I'm assuming the "N" is nitrogen. I know that most all fertilizers have nitrogen in them. Are you suggesting adding only nitrogen, if so where can it be purchased? The remaining 10% of the yard has clover, violets and unfortunatly crabgrass. I have used weed controllers in the past (Amine with 2,4-D) with moderate success with dandelions and clover and other broadleaf weeds. What do you suggest for those violets ?
Answer: We always make fertilizer recommendations by pounds on N/1000 sq ft because the N is the most important nutrient for turf. However, as a rule of thumb, you apply Nitrogen, Phosphorus, and Potassium in about a 4-1-2 ratio on an annual basis. This means that if you apply 4 lbs N/1000/yr, you should apply about 1 lb. P and 2 lb. K/1000/yr. It's not absolutely necessary to apply a fertilizer with a 4-1-2 ratio of nutrients every time, but you should end up with about a 4-1-2 ratio at the end of the year. If you are still looking, there are a number of fertilizers available with only N such as urea (46-0-0).
Having only 10% of the yard with weeds isn't too bad, especially if you are working with over an acre. Be sure to mow at 3" or more which will control most of the weeds. For the broadleaf weeds like dandelion, etc., use a herbicide in mid-October. There are several herbicides that are readily available at garden centers. This application should control almost all of your broadleaf weeds, but be patient because you won't notice the typical curling of the weeds before winter. The weeds will die over the winter. If you have violets next spring, apply the same product in late April, early May. If crabgrass continues to be a problem, try a pre-emergence herbicide in the spring, but I would apply only to the trouble spots that you have had in the past. That way you save money and reduce needless pesticide use.